function validate_email(field, alerttxt) {
 with(field) {
  apos=value.indexOf("@");
  dotpos=value.indexOf(".");
  if(apos < 1 || dotpos - apos < 2) {
   alert(alerttxt); return false;
  } else {
   return true;
  }
 }
}

function validate_form(thisform) {
 with(thisform) {
  if(validate_email(email, "Not a valid e-mail address!") == false) {
   email.focus(); return false;
  }
 }
}